The present invention relates to optical imaging and, more particularly, to systems, processes and products involving episcopic imaging, i.e. imaging utilizing light generally reflected from or at a copy sheet or other visual subject, as distinguished frm diascopic imaging, i.e. imaging utilizing light generally directed through a copy sheet. The present invention is directed primarily to large copy projectors, exemplified by so-called "overhead" and "opaque" projectors. Diascopic overhead projectors have been characterized by: bulky hardware that obtrudes between the audience and the projected image and causes the operator to assume an unnatural posture in order not to obtrude between the projection lens and the screen; and transparencies that are uncomfortable for the operator to view, handle and store. Episcopic overhead projectors theoretically are more compact than diascopic overhead projectors because illuminating source and imaging lens are at the same side of the copy sheet, whereby vertical dimensions are reduced. But, in practice, episcopic overhead projectors also have been obtrusive because either (1) the light source and imaging lens are positioned by a post in a sizeable casing above the copy sheet or (2) a bulky housing envelops the light paths to and from the copy sheet in order to control glare. Episcopic copy, when composed of paper or sheeting of equivalent appearance, has not been adapted for brilliant imaging because of its optical diffusivity.
The primary objects of the present invention are the provision of systems, processes and products involving a portable projector and a copy sheet assemblage that are particularly interrelated to achieve, during projection, direct visual and manual access to the copy sheet by the operator, absolute shielding of the operator and the audience from illuminating light, no interposition of the optical projection system above the level of the copy sheet between the audience and the screen, and natural posture of the operator at the projector. The optical projector comprises a low profile housing in which are positioned an upper window for supporting the copy sheet with its front face upward for direct viewing, a source of illuminating light from which the exterior of the housing is absolutely shielded by the copy sheet itself, and a folded optical path below the window to an imaging lens at the side of the projector. The arrangement is such that an unusually powerful illuminating lamp is practicable. The copy sheet is characterized by a laminated sequence of strata including an upper diffusely reflecting stratum, an intermediate specularly reflecting stratum and a lower self-supporting optically clear polymeric stratum. The specularly reflecting stratum can be marked by applying to the diffusely reflecting stratum a pen containing a chemical reactant that permeates through the diffusely reflecting stratum and changes the optical character of the specularly reflecting stratum. Thus the copy sheet is capable of registering markings that are produced from above but are accessible to the optical system from below. Corrections can be made by a chemical etching patch which can clear sections of the diffusely reflecting and specularly reflecting strata by virtue of a lower optically clear adhesive stratum containing a chemical reactant and present a fresh upper specularly reflective stratum for marking and projection.
Other objects of the present invention will in part be obvious and will in part appear hereinafter.
The invention accordingly comprises the systems, processes and products, together with their components, steps, parts and interrelationships, which are exemplified by the present disclosure, the scope of which will be indicated in the appended claims.